A superconductive wire rod has great electric-power transmission capability even at a low voltage because the electrical resistance thereof converges close to zero at a given temperature.
A superconductive cable having such a superconductive wire rod adopts a cooling method using a refrigerant such as, for example, nitrogen and/or a thermal insulation method of forming a vacuum layer, in order to create and maintain a cryogenic environment.
Such a superconductive cable may generally include a superconductive conductor layer formed of a superconductive wire rod for electric power transmission and a superconductive shield layer for shielding, for example, electromagnetism induced by the superconductive conductor layer. The superconductive shield layer is also formed of a high-cost superconductive wire rod, like the superconductive conductor layer.
That is, electromagnetic waves, induced by electric power transmitted through the superconductive conductor layer, may be shielded by the superconductive shield layer.
A first-generation BSCCO-based superconductive wire rod developed to date may be manufactured via a relatively simple mechanical processing method. However, such a BSCCO-based (Bi-2233 or Bi-2212) superconductive wire rod has a limitation in that a critical current density (Jc) may not be increased to one hundred thousand A/cm2 or more at a temperature of 77K due to the crystal orientation thereof, and it is difficult to achieve a lower production cost for a given performance thereof because the price of Ag, which is the sheath material of the wire rod, is high. Therefore, recently, the first-generation superconductive wire rod has not been widely manufactured or used.
Meanwhile, a second-generation superconductive wire rod includes multiple oxide layers deposited on a metal substrate, and thus is called a coated conductor (hereinafter referred to as “CC”).
A second-generation YBCO- or REBCO-based superconductive wire rod exhibits high critical current in a magnetic field and a critical current density that is dozens of times higher than the first-generation BSCCO-based wire rod. Therefore, it has been focused on since the early 1990s as a next-generation superconductive wire rod that may substitute for the first-generation high-temperature superconductive wire rod, and various manufacturing processes thereof have actively been developed.
Such a second-generation superconductive wire rod may generally include several thin oxide layers and protective layers deposited on a metal substrate. Since the flow of supercurrent in the second-generation superconductive wire rod is limited at the grain boundary, in order to ensure the flow of a great quantity of supercurrent, it is important to improve crystal orientation by biaxially aligning crystal grains of the superconductive wire rod during the processing thereof. The second-generation superconductive wire rod is mainly formed by depositing a YBCO or REBCO (RE=Sm, Gd, Nd, Dy, Ho) material, and the superconductive characteristics of the second-generation superconductive wire rod greatly depend on, for example, the composition, density, and crystal orientation of a superconducting layer included in the produced superconductive wire rod.
A metal substrate provided in the second-generation superconductive wire rod is formed using any of different materials according to the deposition method of a buffer layer. A Hastelloy (an alloy such as SUS) substrate or a Ni—W alloy substrate in which metal crystals are bi-axially oriented in advance via rolling and recrystallization heat treatment (Rolling Assisted Biaxially Textured Substrate (RABiTS)) is representatively used.
When, for example, the Ni—W alloy substrate formed of a magnetic substance is used as the metal substrate of the second-generation superconductive wire rod, alternating current (AC) loss may occur during the transmission of AC power by a superconductive cable.
A superconductive cable using a superconductive wire rod may generally include a superconductive conductor layer formed of a superconductive wire rod for electric-power transmission and a superconductive shield layer for shielding, for example, electromagnetism induced by the superconductive conductor layer.
Recently, the superconductive cable may often be configured such that each of the superconductive conductor layer and the superconductive shield layer is formed of superconductive wire rods in multiple layers, in order to increase electric-power transmission capability.
When each of the superconductive conductor layer and the superconductive shield layer is formed of the superconductive wire rods in multiple layers, AC loss may be further worsened according to the direction or orientation of a metal substrate and a superconducting layer of the superconductive wire rod in each layer.
With regard to the AC loss of the superconductive wire rod, although Japanese Patent Laid-Open Publication No. JP 2012-256508 discloses a technique of minimizing AC loss by reducing the width of a superconductive wire rod of a superconductive conductor layer, no realization or suggestion for a technical solution related to the direction or orientation of the superconductive wire rod is presented in a concrete way. Japanese Patent Registration No. JP 5192741 discloses a technical object and a technical solution related to AC loss, but is very different from the present invention as to the technical solution thereof, and the effect thereof is also questionable. In addition, Japanese Patent Registration No. JP 5385746 discloses the structure of layers of a superconductive wire rod constituting a superconductive cable, but provides no realization or suggestion for a technical solution to achieve a technical object of the present invention.